1. Field of the Invention
This invention relates to an electrophotographic belt (belt for electrophotography) such as a transfer material transport belt or an intermediate transfer belt, used in image forming apparatus which utilize electrophotographic systems, i.e., what are called electrophotographic apparatus, and also relates to an electrophotographic apparatus having the electrophotographic belt, and a process for producing the electrophotographic belt. Monochrome or color (inclusive of full-color) copying machines and printers (such as LBPs) are available as electrophotographic apparatus having electrophotographic belts.
2. Related Background Art
In order to stably reproduce high-grade images by using an electrophotographic apparatus having an electrophotographic belt, it is important to balance the volume resistivity of the electrophotographic belt and the surface resistivity of the surface of the electrophotographic belt on which a toner image or a transfer material is held.
Specifically, taking as an example the case of an intermediate transfer belt, the intermediate transfer belt is required to surely hold on its surface toner images primarily transferred from an electrophotographic photosensitive member, and is further required to allow the toner images held on its surface to be secondarily transferred to a transfer material such as paper in a good efficiency. In order to render such conflicting performances compatible with each other at a high level, it is effective to take into account the balance between volume resistivity and surface resistivity of the intermediate transfer belt.
For example, Japanese Patent Application Laid-open No. H10-228188 discloses that where the surface resistivity and volume resistivity of an intermediate transfer member (such as an intermediate transfer belt) are represented respectively by 10x Ω/square and 10y Ωcm, these are so set as to be 10≦x≦14, y≦13 and x≧y. Then, it discloses that by controlling the volume resistivity and surface resistivity in this way, toner images primarily transferred onto the intermediate transfer belt do not scatter and discharge naturally occurs before subsequent toner images are primarily transferred. It also discloses that the constitution of the intermediate transfer belt may be either of a single-layer structure and a multi-layer structure.
In addition, t is demanded for the electrophotographic belt to have excellent flexing resistance in order to secure good handling properties in the electrophotographic apparatus. It is also demanded for the belt to have excellent wear resistance so that as a result of wear, the surface of the electrophotographic belt for holding toner images or a transfer material is not changed in physical properties or in electrical properties required as the electrophotographic belt. As a material that may satisfy the above at a high level, for example, curable polyimide may be cited.
The curable polyimide, however, is commonly expensive. Accordingly, in order to obtain a lower-cost electrophotographic belt, the present inventors have made studies on an electrophotographic belt comprising a base layer having a good flexibility, containing a thermoplastic resin, and formed on the base layer a surface layer having good wear resistance. Specifically, they have studied how a cured resin film having a uniform thickness and good adherence to the base layer can be used as the surface layer.
As a result of the studies, the present inventors have realized that the surface layer must be formed in a thickness of 3.0 μm or less in order to prevent the surface layer from, e.g., becoming cracked when the electrophotographic belt is flexed. On the basis of such realization, the present inventors have studied how such preferable electrical properties as disclosed in the above Japanese Patent Application Laid-open No. H10-228188 can be imparted to an electrophotographic belt having on the base layer containing a thermoplastic resin a surface layer composed of a thin cured resin film. Therefore, the present inventors have attempted to add conductive particles to the surface layer so as to balance the volume resistivity and surface resistivity of the electrophotographic belt.
However, the surface resistivity of the surface layer has come to be too low (specifically, 107 Ω/square). Thus, they have failed to impart to the electrophotographic belt the preferable electrical properties disclosed in the above Japanese Patent Application Laid-open No. H10-228188.